stifle has 9 distinct synonyms spread across 5 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is stimulate.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
impair the respiration of or obstruct the air passage of
“The foul air was slowly suffocating the children”
be asphyxiated; die from lack of oxygen
“The child suffocated under the pillow”
Synonyms, antonyms and the broader and narrower relations for stifle come from Princeton University’s WordNet. Full sources and licences.